This invention relates to information storage systems and in particular to information recording or reading systems having means for removing debris from a magnetic head transducer.
In recording or reading information on a moving information storage media, such as a magnetic recording disc, relative motion between a magnetic head transducer used for reading and writing information and the storage media on which information is written on and read from is required. The relative velocity between the head and media interface may be, for example, 550 IPS for video and high density digital applications. To achieve maximum performance, an interface of intimate contact is provided between the head and media surface without destruction or excessive wear of the magnetic flux responsive coating on the surface.
As contact pressure between the head and media is increased to improve performance, both media and head wear are increased. The problem is particularly severe in video applications and compounded with medias utilized for storing single video frames on separate tracks of a magnetic disc wherein one track at a time is continuously in contact with the head to provide a continuous stationary display of a single frame. In only five minutes of playtime revolving at 3,600 RPM, for example, a track on the disc is scraped about 18,000 times by the head; the by-products are so hard and abrasive that the same materials are commonly used as lapping compounds.
To prevent failure caused by contact between the head and disc, lubricated surfaces and/or air film separations have been used. However, any separation between the head and disc caused by such lubrication fluid or air film imposes a loss of signal and hence performance. A head/disc separation equal to one wave length could cause about 54.6 dB loss in the output of the replay head. Since it is desired to record wave lengths that approach 1.75 microns, the playback head voltage is reduced to 50% by only 0.19 micron of separation. On the other hand, as discussed above, reduction of separation to meet desired performance would cause the interface to be destroyed within a few seconds.
Prior art solutions to the head-to-disc interface problem have generally been of two types: flying heads in conjunction with rigid hard-surface discs and heads having large surface areas buried in soft flexible "floppy" discs. Flying head discs are very expensive and require complicated and expensive recording/playback systems. A flexible or so-called "floppy" disc reduces the handling and cost problems incurred in the flying head, rigid-disc systems. Some record/read heads for "floppy" discs are relatively large to provide an interface comprised of a large contoured head buried in the soft flexible media. The large record/read head surface area distributes the force per unit area to reduce media wear and separation loss. As the media is moved past the head, however, air collects between the head and disc surface to form an air film. The thickness of this air film is a function of head and media surface finishes, media stiffness, head-media penetration, head size, head surface contour, viscosity of the air and disc-head relative velocity. Because of these restraints, most flexible or "floppy" disc applications are limited to slow speed, low bandwidth digital computer applications or voice recording systems.
In information storage systems using rigid discs, catastrophic failures may occur due to the presence of small contaminants (on the order of 0.01 mm or 10 microns) which accumulate on the disc and head. These contaminants cause head crashes which result in permanent damage to the recording head, thereby necessitating head replacement. Floppy disc systems are also susceptible to catastrophic failures due to head crashes caused by the presence of small debris. Small pressure pads are often used in these floppy disc systems to remove debris and other contaminants. In information storage systems using compliant discs, catastrophic failures and head crashes are not so common because the disc is able to change shape to maintain good head to disc contact. One such system is shown in U.S. Pat No. 4,079,427. Nevertheless, debris may build up on a recording head which interferes with a laminar flow of air across the head and prevents the intimate head-to-disc contact required for effective recording and playback of information. This invention relates to an improved head cleaning cartridge and an apparatus for automatically executing a head cleaning routine.